Second‐Harmonic‐Generation Circular‐Dichroism in Chiral Perovskite Single Crystals Enhanced by Self‐Trapped Excitonic State

Abstract The inherent non‐centrosymmetry and circular dichroism of chiral perovskites endow them with immense potential for nonlinear optical applications. The exploration of chiral perovskite single crystals with high degree of polarization in second harmonic generation (SHG) is pivotal for the development of frequency conversion devices. Herein, ( R / S ‐BrsBA) 2 PbBr 4 (BrsBA is 4‐bromo‐2‐butylammonium) single crystals are synthesized, which exhibit robust SHG responses with both high linear polarization and high sensitivity to circularly‐polarized incident light. Through temperature and magnetic field dependent photoluminescence spectroscopy, the study reveals a resonant enhancement relationship between self‐trapped exciton and SHG circular dichroism. Notably, under this resonant enhancement conditions, the crystals demonstrate a high circularly polarized SHG anisotropy factor of 0.64. These results not only deepen the understanding of SHG mechanism in chiral perovskites but also pioneers new pathways for their applications in nonlinear chiral optics.